Lateral meniscus

Original Editor - Aarti Sareen

Top Contributors - Aarti Sareen, Evan Thomas, Rachael Lowe, Oyemi Sillo and Fasuba Ayobami

Introduction

The word menisci are derived from the Greek work meniskos, which means "crescent". At knee joint the menisci plays a major role in congurency of the joint. Menisci forms the concavity in which the femoral condyles sits. Menisci rests between the thigh bone femur and the tibia and there are two knee joint ligaments. They are a type of cartilage in the joint. The rubbery texture of the menisci is due to their fibrocartilagenous structure. Their shape is maintained by the collagen within them. One meniscus is on the inner side of your knee--the medial meniscus. The other meniscus is on the outer side of your knee - the lateral meniscus.

Lat.meniscus.gif

Anatomy and attachment

The lateral meniscus is almost circular and covers a larger portion of the tibial articular surface than the medial meniscus. The lateral meniscus is consistent in width throughout its course. The anterior horn of the lateral meniscus blends into the attachment of the anterior cruciate ligament, whereas the posterior horn attaches just behind the intercondylar eminence, often blending into the posterior aspect of the ACL. There is no attachment of the lateral meniscus to the LCL. Its peripheral attachment is interrupted posterior to where the popliteal tendon passes. The capsular components attach the lateral meniscus to the tibia less firmly than the medial meniscus. The lateral meniscus is more mobile than the
medial meniscus, and has a range of movement that may be as great as 10 mm (0.4 in) in an anteroposterior direction. This mobility is explained by the close proximity of the attachments of the anterior and posterior horns and the lack of attachment to the capsular ligament posterolaterally. The firm attachment of the arcuate ligament to the lateral meniscus and the attachment of the popliteus muscle to both the arcuate ligament and meniscus ensure the dynamic retraction of the posterior segment of the meniscus during internal rotation of the tibia on the femur as the knee begins to flex from its fully extended position.

Knee-joint-meniscus.jpg

VASCULAR SUPPLY:

The vascular supply of the menisci originates predominately from the inferior and superior lateral and medial genicular arteries. During the first year of life the meniscus contains blood vessels throughout its body but when the weight bearing starts the vascularity and the circulatory network diminish and only 25-33% area remain vascular by the capillaries of the capsule and synovial membrane[1]. The vascularity diminishes so much that in 4th decade of life only the periphery is vascular whereas the center of the menisci is avascular. The center portion is completely dependent upon the synovial fluid diffusion for nutrition [2]. The central avascular portion of menisci either does not heal completely or heal at all after injury[1].

Meniscus-blood-supply-zones.jpg
Meniscal blood supply.gif

NERVE SUPPLY:

The horns of the menisci and the peripheral vascularized portion of the meniscal bodies are well innervated with free nerve endings (nociceptors) and three different mechanoreceptors (Ruffini corpuscles, pacinian corpuscles, and Golgi tendon organs)[1][3][4].

Injury/Tear

The most common mechanism of menisci injury is a twisting injury with the foot anchor on the ground, often by another player's body. A slow twisting force may also cause the tear.Damage to the meniscus is due to rotational forces directed to a flexed knee (as may occur with twisting sports) is the usual underlying mechanism of injury[5][6].

The meniscal tear is of following types:

  • Longitudinal
  • Radial
  • Bucket handle
  • Flap
  • Horizontal cleavage
  • Degenerative
Types of meniscal tears.jpg

The patient comes up with major complain of knee pain, swelling and knee locking which is when the patient is unable to straighten the leg fully. This can be accompanied by a clicking feeling. A valgus force i.e hyperflexion of the knee and also on internal rotation of the foot and the lower leg in relation to the femur when the knee joint is flexed to 70–90° cause the lateral meniscal tear.[6]

The diagnosis of a lateral meniscus injury is considered to be fairly certain if three or more of the following findings are present:[5]
– tenderness at one point over the lateral joint line;
– pain in the area of the lateral joint line during hyperextension of the knee joint;
– pain in the area of the lateral joint line during hyperflexion of the knee joint;
– pain during internal rotation of the foot and the lower leg when the knee is flexed at different angles;
– weakened or hypotrophied quadriceps muscle.

Diagnosis

Diagnosis can be made on the basis of:

  • Special test
  • X-ray
  • MRI

Special Tests:

Although there are several tests for a meniscus tear, none can be considered definitive without considerable experience on the part of the examiner. Patient history and the mechanism of injury also provide a major source of information. The most commonly used special tests are...

X-Ray:

X-ray is done in weight-bearing but is not helpful in detecting the medial meniscal tear, but, can detect other associated conditions at bony level.

Magnetic Resonance Imaging:

Meniscal tear can be well appreciated on an MRI.

Resources

References

  1. 1.0 1.1 1.2 Gray JC: Neural and vascular anatomy of the menisci of the human knee. J Orthop Sports Phys Ther 29:23–30, 1999.
  2. McCarty EC, Marx RG, DeHaven KE: Meniscus repair: Considerations in treatment and update of clinical results. Clin Orthop 402:122–134, 2002.
  3. Zimny ML, Albright DJ, Dabezies E: Mechanoreceptors in the human medial meniscus. Acta Anat (Basel) 133:35–40, 1988.
  4. Mine T, Kimura M, Sakka A, et al.: Innervation of nociceptors in the menisci of the knee joint: An immunohistochemical study. Arch Orthop Trauma Surg 120:201–204, 2000.
  5. 5.0 5.1 Peterson,Renström. SPORTS INJURIES:Their Prevention and Treatment.Third Edition.
  6. 6.0 6.1 Brunker,Khan.Clinical Sports Medicine.3rd Edition.